The following publications are believed to represent the current state of the art:
U.S. Pat. Nos.: 3,168,465; 4,632,758; 4,780,198; 4,919,815; 5,196,111; 5,578,214; 5,788,838; 5,855,785; 6,063,273; 6,623,640; 6,758,886 and 7,022,226;
European Patent No.: 0 382 340;
http://www.paques.nl/?pid=245&parentid=41, which describes the Paques BIOPAQ® UASB+ system; and
http://www.paques.nl/?pid=44&parentid=41, which describes the Paques BIOPAQ® UBOX system.